// SAX document handler.
// No warranty; no copyright -- use this as you will.
// $Id: DocumentHandler.java,v 1.5 1998/05/01 20:46:02 david Exp $

package org.xml.sax;

/**
  * Receive notification of general document events.
  *
  * <p>This is the main interface that most SAX applications
  * implement: if the application needs to be informed of basic parsing 
  * events, it implements this interface and registers an instance with 
  * the SAX parser using the setDocumentHandler method.  The parser 
  * uses the instance to report basic document-related events like
  * the start and end of elements and character data.</p>
  *
  * <p>The order of events in this interface is very important, and
  * mirrors the order of information in the document itself.  For
  * example, all of an element's content (character data, processing
  * instructions, and/or subelements) will appear, in order, between
  * the startElement event and the corresponding endElement event.</p>
  *
  * <p>Application writers who do not want to implement the entire
  * interface can derive a class from HandlerBase, which implements
  * the default functionality; parser writers can instantiate
  * HandlerBase to obtain a default handler.  The application can find
  * the location of any document event using the Locator interface
  * supplied by the Parser through the setDocumentLocator method.</p>
  *
  * @author David Megginson (ak117@freenet.carleton.ca)
  * @version 1.0
  * @see org.xml.sax.Parser#setDocumentHandler
  * @see org.xml.sax.Locator
  * @see org.xml.sax.HandlerBase
  */
public interface DocumentHandler {


  /**
    * Receive an object for locating the origin of SAX document events.
    *
    * <p>SAX parsers are strongly encouraged (though not absolutely
    * required) to supply a locator: if it does so, it must supply
    * the locator to the application by invoking this method before
    * invoking any of the other methods in the DocumentHandler
    * interface.</p>
    *
    * <p>The locator allows the application to determine the end
    * position of any document-related event, even if the parser is
    * not reporting an error.  Typically, the application will
    * use this information for reporting its own errors (such as
    * character content that does not match an application's
    * business rules).  The information returned by the locator
    * is probably not sufficient for use with a search engine.</p>
    *
    * <p>Note that the locator will return correct information only
    * during the invocation of the events in this interface.  The
    * application should not attempt to use it at any other time.</p>
    *
    * @param locator An object that can return the location of
    *                any SAX document event.
    * @see org.xml.sax.Locator
    */
  public abstract void setDocumentLocator (Locator locator);


  /**
    * Receive notification of the beginning of a document.
    *
    * <p>The SAX parser will invoke this method only once, before any
    * other methods in this interface or in DTDHandler (except for
    * setDocumentLocator).</p>
    *
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    */
  public abstract void startDocument ()
    throws SAXException;


  /**
    * Receive notification of the end of a document.
    *
    * <p>The SAX parser will invoke this method only once, and it will
    * be the last method invoked during the parse.  The parser shall
    * not invoke this method until it has either abandoned parsing
    * (because of an unrecoverable error) or reached the end of
    * input.</p>
    *
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    */
  public abstract void endDocument ()
    throws SAXException;


  /**
    * Receive notification of the beginning of an element.
    *
    * <p>The Parser will invoke this method at the beginning of every
    * element in the XML document; there will be a corresponding
    * endElement() event for every startElement() event (even when the
    * element is empty). All of the element's content will be
    * reported, in order, before the corresponding endElement()
    * event.</p>
    *
    * <p>If the element name has a namespace prefix, the prefix will
    * still be attached.  Note that the attribute list provided will
    * contain only attributes with explicit values (specified or
    * defaulted): #IMPLIED attributes will be omitted.</p>
    *
    * @param name The element type name.
    * @param atts The attributes attached to the element, if any.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see #endElement
    * @see org.xml.sax.AttributeList 
    */
  public abstract void startElement (String name, AttributeList atts)
    throws SAXException;


  /**
    * Receive notification of the end of an element.
    *
    * <p>The SAX parser will invoke this method at the end of every
    * element in the XML document; there will be a corresponding
    * startElement() event for every endElement() event (even when the
    * element is empty).</p>
    *
    * <p>If the element name has a namespace prefix, the prefix will
    * still be attached to the name.</p>
    *
    * @param name The element type name
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    */
  public abstract void endElement (String name)
    throws SAXException;


  /**
    * Receive notification of character data.
    *
    * <p>The Parser will call this method to report each chunk of
    * character data.  SAX parsers may return all contiguous character
    * data in a single chunk, or they may split it into several
    * chunks; however, all of the characters in any single event
    * must come from the same external entity, so that the Locator
    * provides useful information.</p>
    *
    * <p>The application must not attempt to read from the array
    * outside of the specified range.</p>
    *
    * <p>Note that some parsers will report whitespace using the
    * ignorableWhitespace() method rather than this one (validating
    * parsers must do so).</p>
    *
    * @param ch The characters from the XML document.
    * @param start The start position in the array.
    * @param length The number of characters to read from the array.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see #ignorableWhitespace 
    * @see org.xml.sax.Locator
    */
  public abstract void characters (char ch[], int start, int length)
    throws SAXException;


  /**
    * Receive notification of ignorable whitespace in element content.
    *
    * <p>Validating Parsers must use this method to report each chunk
    * of ignorable whitespace (see the W3C XML 1.0 recommendation,
    * section 2.10): non-validating parsers may also use this method
    * if they are capable of parsing and using content models.</p>
    *
    * <p>SAX parsers may return all contiguous whitespace in a single
    * chunk, or they may split it into several chunks; however, all of
    * the characters in any single event must come from the same
    * external entity, so that the Locator provides useful
    * information.</p>
    *
    * <p>The application must not attempt to read from the array
    * outside of the specified range.</p>
    *
    * @param ch The characters from the XML document.
    * @param start The start position in the array.
    * @param length The number of characters to read from the array.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    * @see #characters
    */
  public abstract void ignorableWhitespace (char ch[], int start, int length)
    throws SAXException;


  /**
    * Receive notification of a processing instruction.
    *
    * <p>The Parser will invoke this method once for each processing
    * instruction found: note that processing instructions may occur
    * before or after the main document element.</p>
    *
    * <p>A SAX parser should never report an XML declaration (XML 1.0,
    * section 2.8) or a text declaration (XML 1.0, section 4.3.1)
    * using this method.</p>
    *
    * @param target The processing instruction target.
    * @param data The processing instruction data, or null if
    *        none was supplied.
    * @exception org.xml.sax.SAXException Any SAX exception, possibly
    *            wrapping another exception.
    */
  public abstract void processingInstruction (String target, String data)
    throws SAXException;

}
